Hypercholesterolemia is known to be one of the prime risk factors for ischemic cardiovascular disease, such as arteriosclerosis. Bile acid sequestrants have been used to treat this condition; they seem to be moderately effective but they must be consumed in large quantities, i.e. several grams at a time and they are not very palatable.
Mevacor (lovastatin), now commercially available, is one of a group of very active antihypercholesterolemic agents that function by limiting cholesterol biosynthesis by inhibiting the enzyme, HMG-CoA reductase. In addition to the natural fermentation products, mevastatin and lovastatin, there are a variety of semi-synthetic and totally synthetic analogs thereof.
The naturally occurring compounds and their semi-synthetic analogs have the following general structural formulae: ##STR1## wherein:
R.sup.3 is hydrogen, C.sub.1-5 alkyl or C.sub.1-5 alkyl substituted with a member of the group consisting of phenyl, dimethylamino, or acetylamino; and
R.sup.4 is ##STR2## wherein Q is ##STR3## R.sup.5 is H or OH; M is ##STR4## R.sup.6 is hydrogen or hydroxy;
R.sup.7 is hydrogen or methyl; and a, b, c, and d represent single bonds, one of a, b, c or d represents a double bond, or both a and c or both b and d represent double bonds provided that when a is a double bond, Q is ##STR5## and when d is a double bond, M is ##STR6##
U.S. Pat. No. 4,517,373 discloses semi-synthetic hydroxy containing compounds represented by the above general formula wherein R.sup.4 is ##STR7##
U.S. Pat. No. 4,537,859 and U.S. Pat. No. 4,448,979 also disclose semi-synthetic hydroxy-containing compounds represented by the above general formula wherein R.sup.4 is ##STR8##
These compounds are prepared by the action of certain microorganisms on the corresponding non-hydroxylated substrates. One such organism described in U.S. Pat. No. 4,537,859 is of the genus Nocardia.
U.S. Pat. No. 4,376,863 discloses a fermentation product, isolated after cultivation of a microorganism belonging to the genus Aspergillus, which has a hydroxy containing butyryloxy side chain and is represented by the above general formula wherein R.sup.4 is ##STR9##
Japanese unexamined patent application J59-122,483-A discloses a semi-synthetic hydroxy-containing compound represented by the above general formula wherein R.sup.4 is ##STR10##
Copending U.S. patent application Ser. No. 048,136 filed May 15, 1987 discloses 6-substituted compounds of the above general formula wherein R.sub.4 is ##STR11## wherein R is CH.sub.2 OH, ##STR12## CO.sub.2 R.sup.4 or ##STR13## and R.sup.1, R.sup.3, R.sup.4, R.sup.6 and R.sup.7 are broadly defined organic moieties.
The compounds of the above-mentioned U.S. patent application, Ser. No. 048,136 wherein a and c are double bonds were prepared by a microbiological conversion of lovastatin or an analog thereof with a 6-methyl substituent. Compounds where one of a, b or c represent a double bond or a, b, c all represent single bonds were prepared by a synthetic sequence from the 8-hydroxy-6-methyl derivative.
The literature discloses a reaction known as the Barton Reaction by which a hydrogen in the .delta. position to an OH group can be abstracted to afford a carbon radical which can be oxidized. (See Hesse Adv. Free-Radical Chem. 3, 83-137 (1969); Barton, Pure Appl. Chem. 16, 1-15 (1968); Arthar, Adv. Photochem. 2, 263-304 (1964).